1. Field of the Invention
The present invention relates to resistive materials for a microbolometer, a method for preparation of resistive materials, and a microbolometer containing the resistive materials, and more particularly to using an alloy of silicon and antimony or an alloy of silicon, antimony and germanium as resistive materials for a microbolometer.
This work was supported by the IT R&D program of MIC/IITA [2006-S-054-02, Development of multifunctional sensor technology of CMOS-based micro electro mechanical system (MEMS) for Ubiquitous].
2. Discussion of Related Art
To sense infrared, various methods are used according to infrared wavelength ranges to be sensed.
To sense near infrared, a photon-type infrared sensor is used. The photon-type infrared sensor, which uses a photovoltaic effect of a semiconductor to sense a photon due to absorbed infrared, has advantages of good sensitivity and short response time. However, the photon-type infrared sensor has a defect of requiring a cryogenic cooling system when operating at the highest sensitivity.
On the other hand, in the case of a sensor of sensing mid or far infrared, a device capable of sensing heat generated by infrared has been generally used. The infrared sensor capable of sensing heat is classified into a bolometer type, a thermocouple type, and a pyroelectric type according to sensing method. Although the heat-type infrared sensor has lower sensitivity and longer response time than the photon-type infrared sensor, it has attracted attention for its aptness for minimization and various applications since the heat-type infrared sensor does not need the cryogenic cooling system. Generally, such a no-cooling infrared sensor senses an infrared wavelength that ranges from 8 to 14 microns. To manufacture the no-cooling infrared sensor, a substrate and a multilayer membrane structure having a certain thickness (i.e., a thickness corresponding to a quarter of a center wavelength) are needed. Such a membrane includes an absorbing layer, an insulating layer, a resistive layer, an electrode layer, etc. Among them, the resistive layer may govern the performance of the microbolometer.
At the present time, vanadium oxide is most used resistive material for the microbolometer. V2O5 and VO2 are the most commonly used compositions. Between them, VO2 is employed as the resistive material for the microbolometer.
Vanadium oxide shows various values of a temperature coefficient of resistance (TCR) according to oxygen content and metal components used in doping. If VO2 whose oxygen content is properly adjusted is used as the resistive material, it is known that a TCR is approximately −2 to −4% K. Further, it is also known that there is little Johnson noise since a fabricated thin film has relatively low resistance, and noise due to frequency variation is very low.
Generally, a sputtering method is used for producing vanadium oxide. In the case of VO2, it is very difficult to precisely adjust the composition. Because of such process characteristics, it is very hard to apply a semiconductor batch process to a matching process with a micro electro mechanical system (MEMS) structure.
Meanwhile, to overcome the difficulty in the process using vanadium oxide, research into a microbolometer that employs amorphous silicon as the resistive material has been carried out. However, the resistive material of amorphous silicon shows a TCR lower than that of vanadium oxide, and a high resistance having an effect on noise when a signal is reproduced. In the case of the microbolometer produced by Texas Instrument Incorporated and L-3 Company, it has been reported that the resistance thereof reaches 10 to 30 MΩ if the thickness of amorphous silicon ranges from 100 to 200 nm. However, such a resistance causes 1/f noise, and thus the performance of the microbolometer is deteriorated. Further, a low resistance allows a higher degree of freedom when designing a read out integrated circuit (ROIC) for processing a signal generated by the infrared sensor.
Accordingly, the present invention proposes a silicon alloy, which lowers the resistance while maintaining the TCR close to that of vanadium oxide, as the resistive material for the microbolometer